[bug #68459] Optimize "isprimelarge.cc" on systems with native 128-bit arithmetics

"Dmitri A. Sergatskov" <[email protected]> Thu, 18 Jun 2026 16:29:42 -0400 (EDT)

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Message-ID	<[email protected]>

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URL:
  <https://savannah.gnu.org/bugs/?68459>

                 Summary: Optimize "__isprimelarge__.cc" on systems with
native 128-bit arithmetics
                   Group: GNU Octave
               Submitter: dasergatskov
               Submitted: Thu 18 Jun 2026 08:29:39 PM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Performance
                  Status: None
             Assigned to: None
         Originator Name:
        Originator Email:
             Open/Closed: Open
         Discussion Lock: Unlocked
                 Release: dev
        Operating System: Any
           Fixed Release: None
         Planned Release: None


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Follow-up Comments:


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Date: Thu 18 Jun 2026 08:29:39 PM UTC By: Dmitri A. Sergatskov <dasergatskov>
On most 64-bit systems gcc and clang (and, I assume, its derivatives like
Intel compiler) support wide integer type (int128). On those systems it is
possible to optimize "__isprimelarge__.cc" by doing "mod (a*b, modulus)"
without overflow.

I will post CSET shortly.

Dmitri.
-- 








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